Is double-braced scalar initialization allowed by the C++ standard?

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I have the following code:



int x = ;


Is this syntax valid according to the C++ standard? (I'm interested in C++11 and later.)



When using the latest compilers there is no problem, however in some older ones (e.g. GCC 4.8.5) it gives following error:




error: braces around scalar initializer for type 'int'





c++ c++11 language-lawyer




share|improve this question


























    up vote
    31
    down vote

    favorite
    2












    I have the following code:



    int x = ;


    Is this syntax valid according to the C++ standard? (I'm interested in C++11 and later.)



    When using the latest compilers there is no problem, however in some older ones (e.g. GCC 4.8.5) it gives following error:




    error: braces around scalar initializer for type 'int'





    c++ c++11 language-lawyer




    share|improve this question
























      up vote
      31
      down vote

      favorite
      2









      up vote
      31
      down vote

      favorite
      2






      2





      I have the following code:



      int x = ;


      Is this syntax valid according to the C++ standard? (I'm interested in C++11 and later.)



      When using the latest compilers there is no problem, however in some older ones (e.g. GCC 4.8.5) it gives following error:




      error: braces around scalar initializer for type 'int'





      c++ c++11 language-lawyer




      share|improve this question














      I have the following code:



      int x = ;


      Is this syntax valid according to the C++ standard? (I'm interested in C++11 and later.)



      When using the latest compilers there is no problem, however in some older ones (e.g. GCC 4.8.5) it gives following error:




      error: braces around scalar initializer for type 'int'






      c++ c++11 language-lawyer





      share|improve this question













      share|improve this question




      share|improve this question








      edited Aug 29 at 13:00









      Boann

      35.6k1184116




      35.6k1184116










      asked Aug 29 at 10:34









      Igor

      35939




      35939






















          1 Answer
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          up vote
          33
          down vote



          accepted










          This is ill-formed. gcc is wrong to accept it and clang seems to allow it as an extension, as it warns about it.



          I'm going to quote the latest draft, but it doesn't make a difference. List initialization works as follows as per [dcl.init.list], where T is int in this case:



          • If the initializer list is a designated initializer list, [...] => it's not

          • If T is an aggregate class [...] => it's not

          • If T is a character array [...] => it's not.

          • If T is an aggregate [...] => it's not (only arrays and classes are aggregates)

          • If the initializer list has no elements [...] => it doesn't

          • If T is a specialization of std::initializer_list [...] => it's not

          • If T is a class type [...] => it's not

          • If T is an enumeration with fixed underlying type [...] => it's not

          • If the initializer list has a single element of type E [...] => a braced initializer list has no type, so no

          • If T is a reference type [...] => it isn't

          • If the initializer list has no elements [...] => it doesn't

          • Otherwise the program is ill-formed





          share|improve this answer
















          • 4




            +1 and see also core language issue 1501 which follows the same logic as this answer to explicitly say that it's invalid.
            – hvd
            Aug 29 at 11:51










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          1 Answer
          1






          active

          oldest

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          active

          oldest

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          active

          oldest

          votes








          up vote
          33
          down vote



          accepted










          This is ill-formed. gcc is wrong to accept it and clang seems to allow it as an extension, as it warns about it.



          I'm going to quote the latest draft, but it doesn't make a difference. List initialization works as follows as per [dcl.init.list], where T is int in this case:



          • If the initializer list is a designated initializer list, [...] => it's not

          • If T is an aggregate class [...] => it's not

          • If T is a character array [...] => it's not.

          • If T is an aggregate [...] => it's not (only arrays and classes are aggregates)

          • If the initializer list has no elements [...] => it doesn't

          • If T is a specialization of std::initializer_list [...] => it's not

          • If T is a class type [...] => it's not

          • If T is an enumeration with fixed underlying type [...] => it's not

          • If the initializer list has a single element of type E [...] => a braced initializer list has no type, so no

          • If T is a reference type [...] => it isn't

          • If the initializer list has no elements [...] => it doesn't

          • Otherwise the program is ill-formed





          share|improve this answer
















          • 4




            +1 and see also core language issue 1501 which follows the same logic as this answer to explicitly say that it's invalid.
            – hvd
            Aug 29 at 11:51














          up vote
          33
          down vote



          accepted










          This is ill-formed. gcc is wrong to accept it and clang seems to allow it as an extension, as it warns about it.



          I'm going to quote the latest draft, but it doesn't make a difference. List initialization works as follows as per [dcl.init.list], where T is int in this case:



          • If the initializer list is a designated initializer list, [...] => it's not

          • If T is an aggregate class [...] => it's not

          • If T is a character array [...] => it's not.

          • If T is an aggregate [...] => it's not (only arrays and classes are aggregates)

          • If the initializer list has no elements [...] => it doesn't

          • If T is a specialization of std::initializer_list [...] => it's not

          • If T is a class type [...] => it's not

          • If T is an enumeration with fixed underlying type [...] => it's not

          • If the initializer list has a single element of type E [...] => a braced initializer list has no type, so no

          • If T is a reference type [...] => it isn't

          • If the initializer list has no elements [...] => it doesn't

          • Otherwise the program is ill-formed





          share|improve this answer
















          • 4




            +1 and see also core language issue 1501 which follows the same logic as this answer to explicitly say that it's invalid.
            – hvd
            Aug 29 at 11:51












          up vote
          33
          down vote



          accepted







          up vote
          33
          down vote



          accepted






          This is ill-formed. gcc is wrong to accept it and clang seems to allow it as an extension, as it warns about it.



          I'm going to quote the latest draft, but it doesn't make a difference. List initialization works as follows as per [dcl.init.list], where T is int in this case:



          • If the initializer list is a designated initializer list, [...] => it's not

          • If T is an aggregate class [...] => it's not

          • If T is a character array [...] => it's not.

          • If T is an aggregate [...] => it's not (only arrays and classes are aggregates)

          • If the initializer list has no elements [...] => it doesn't

          • If T is a specialization of std::initializer_list [...] => it's not

          • If T is a class type [...] => it's not

          • If T is an enumeration with fixed underlying type [...] => it's not

          • If the initializer list has a single element of type E [...] => a braced initializer list has no type, so no

          • If T is a reference type [...] => it isn't

          • If the initializer list has no elements [...] => it doesn't

          • Otherwise the program is ill-formed





          share|improve this answer












          This is ill-formed. gcc is wrong to accept it and clang seems to allow it as an extension, as it warns about it.



          I'm going to quote the latest draft, but it doesn't make a difference. List initialization works as follows as per [dcl.init.list], where T is int in this case:



          • If the initializer list is a designated initializer list, [...] => it's not

          • If T is an aggregate class [...] => it's not

          • If T is a character array [...] => it's not.

          • If T is an aggregate [...] => it's not (only arrays and classes are aggregates)

          • If the initializer list has no elements [...] => it doesn't

          • If T is a specialization of std::initializer_list [...] => it's not

          • If T is a class type [...] => it's not

          • If T is an enumeration with fixed underlying type [...] => it's not

          • If the initializer list has a single element of type E [...] => a braced initializer list has no type, so no

          • If T is a reference type [...] => it isn't

          • If the initializer list has no elements [...] => it doesn't

          • Otherwise the program is ill-formed






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Aug 29 at 10:48









          Rakete1111

          31.9k973107




          31.9k973107







          • 4




            +1 and see also core language issue 1501 which follows the same logic as this answer to explicitly say that it's invalid.
            – hvd
            Aug 29 at 11:51












          • 4




            +1 and see also core language issue 1501 which follows the same logic as this answer to explicitly say that it's invalid.
            – hvd
            Aug 29 at 11:51







          4




          4




          +1 and see also core language issue 1501 which follows the same logic as this answer to explicitly say that it's invalid.
          – hvd
          Aug 29 at 11:51




          +1 and see also core language issue 1501 which follows the same logic as this answer to explicitly say that it's invalid.
          – hvd
          Aug 29 at 11:51

















           

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